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Introduction to Sexually Transmitted Diseases (STDs)

Sexually transmitted diseases (STDs) refer to a set of clinical infections in which a mode of transmission is through sexual contact, and in which at least one sexual partner is infected. Many of these infections spread predominantly through sexual intercourse, but in some others, sexual contact may play a less predominant or uncertain role. Most STDs are not, however, spread through casual contact, vectors or fomites.

STDs as a whole affect millions of people in the United States and around the world each year, causing significant morbidity and mortality. Although great strides have been made in the last century toward the treatment and control of many STDs, new STDs emerge, and outbreaks of certain diseases make the organisms difficult to control.

There are several approaches to the study of STDs. One is to identify the organism (bacteria, virus, or other) that causes a particular illness. Another is to categorize the symptoms, describe a syndrome, and think of the possible underlying organisms that may be their cause. The first approach offers an excellent way to familiarize oneself with the family of organisms believed to cause STDs. The latter approach is useful in thinking about how the diseases manifest themselves in humans, since clinical symptoms present in a variety of different ways. Moreover, the latter approach is useful because multiple infections in one person are not uncommon.

In addition, the student of STDs must address how the disease is spread throughout the population. The study of diseases in a population is called epidemiology. Understanding the epidemiology of STDs is critical for several reasons. STDs, like many diseases, are transmitted through practice of human behavior. A wide range of social factors thus affects STDs and their spread, including (obviously) sexual habits, migration, war and poverty. Since several STDs present asymptomatically, understanding their epidemiology helps us to target persons who are infected and are spreading the diseases unwittingly. Finally, the epidemiology of STDs informs programs that target STD prevention. This is particularly important, since most STDs caused by viruses are incurable, and many STDs caused by bacteria can render permanent physical damage if not treated early and effectively.

This SparkNote is organized to present STDs in the same order as they are introduced above. First, the separate organisms are discussed and grouped into bacterial, viral and non-bacterial/non-viral infections. These sections contain information about the organisms, their prevalence, and a brief summary of their epidemiology. After you have gained familiarity with some of the organisms and diseases, the epidemiology of STDs as a whole is discussed, along with strategies for their prevention.

This SparkNote does not discuss in detail the medical testing and treatment protocols for the STDs discussed, since they change constantly, and depend on the availability of treatment and the individual patient. The process of diagnosing an STD is better left up to the health care professional. This SparkNote will provide an introduction to the most common STDs by describing them individually. The multiple-choice test at the end of the SparkNote may evaluate your ability to link symptoms with treatment, however.